Fountain solution and plate etch concentrate of increased operating latitude

ABSTRACT

A FOUNTAIN SOLUTION CONCENTRATE OF INCREASED OPERATING LATITUDE IS PROVIDED WHICH IS ADAPTED UPON VARYING DEGREES OF WATER DILUTION FOR USE WITH A PLURALITY OF DIFFERENT TYPES OF PLANOGRAPHIC MASTERS, SUCH AS ELECTROSTATIC, DIRECT INAGE, AND PHOTOGRAPHIC PLATES, BOTH PROJECTION SPEED AND CONVENTIONAL. THE CONCENTRATE COMPRISES AN AQUEOUS SOLUTION OF A HUMECTANT, A HUFFERED PHOSPHATE COMPOUND, AND PREFERABLY A LOW MOLECULAR WEIGHT AIDEHYDE. RELATIVELY HIGH WEIGHT RATIOS OF THE PHOSPHATE ION TO THE HUMECTANT ARE POSSIBLE WITHOUT SACRIFICING A TOLERABLE ACIDIC PH.

United States Patent 3,687,694 FOUNTAIN SOLUTION AND PLATE ETCHCONCENTRATE OF INCREASED OPERAT- ING LATITUDE Charles H. Van Dusen, Jr.,Willoughhy, Ohio, assignor to Addressograph Multigraph Corporation,Cleveland, Ohio No Drawing. Continuation of abandoned application Ser.No. 855,369, Sept. 4, 1969. This application Jan. 18, 1971, Ser. No.107,522

Int. Cl. C09k 3/18 US. Cl. 106-2 4 Claims ABSTRACT OF THE DISCLOSURE Afountain solution concentrate of increased operating latitude isprovided which is adapted upon varying degrees of water dilution for usewith a plurality of different types of planographic masters, such aselectrostatic, direct image, and photographic plates, both projectionspeed and conventional.

The concentrate comprises an aqueous solution of a humectant, a bulferedphosphate compound, and preferably a low molecular weight aldehyde.Relatively high weight ratios of the phosphate ion to the humectant arepossible without sacrificing a tolerable acidic pH.

This application is a continuation of application Ser. No. 855,368,filed Sept. 4, 1969, and now abandoned.

BACKGROUND OF THE INVENTION In the art of copy reproduction fromplanographic mas ters, it is customary continually to flow what istermed a fountain solution over a master as it is rotated on a drum toimprint repeatedly its image on a receiving sheet of paper, or the like,either directly or through an intervening blanket cylinder. The solutionis designed to convert the non-image areas to hydrophilic condition, topreserve that condition in the course of the printing use,

and to maintain a sharp distinction between the hydro-' phobic imageareas and the hydrophilic background areas, such that a longer run maybe achieved than might otherwise be the case.

The present invention relates to a solution concentrafi which can beshipped as and then diluted at a point of use and, more particularly, tosuch a concentrate which, even after varying degrees of dilution, iseffective for use with various types of planographic masters, either asa fountain solution or plate etch, without sacrificing a tolerableacidic pH.

In the past, fountain solutions have been composed of ingredients founduseful for particular planographic masters, especially as new or moresophisticated types of masters appeared. For example, whether thebacking was paper, aluminum, or zinc, coated or uncoated, the type ofsensitizer employed, the manner by which an image was actually formed onthe backing, etc., all could influence the ingredients chosen for afountain solution to be used with such a master. Accordingly, it is notsurprising that a number of different fountain solutions have beenformulated to meet diverse requirements, causing printers to stockinventories of each. It would, therefore, advance the art if a singlefountain solution could be provided which required only varying amountsof dilution to adapt it for virtually any type of master, regardless ofthe nature of the backing, the sensitizer used, and whether aconventional, electrostatic, direct image, or Photo-Direct master was tobe prepared.

It is known that the phosphate ion, EPO4, is admirably suited formaintaining the non-image areas of a master in Patented Aug. 29, 1972ice a hydrophilic condition. The effect of the phosphate ion, as well asthe latitude of application of a fountain solution containing it,particularly a concentrate, are directly related to the amount ofphosphate ion that can be dissolved. Not many phosphate compounds arewater soluble. Those that are have such a limited solubility inglycerin-water solution that for a relatively concentrated solution,such that contemplated for the present fountain solution concentrate,not enough phosphate can be dissolved to meet the objective sought. Onthe other hand, phosphoric acid, H PO is readily soluble in water. Inthis case, however, dissolving enough acid to produce the desired amountof phosphate ion in a concentrate renders the solution so stronglyacidic that it is impractical for use.

Another important component of a fountain solution is a humectant suchas glycerin. A humectant serves not only to keep the surface moist in adry atmosphere, but to keep the solution on the surface of a master andprevent it from soaking in which can result in curling of paper-backedmasters. Similarly, a humectant retains the phosphate ion on thenon-image areas of the master where it can perform its useful andintended functions. Accordingly, it is desirable to have as muchhumectant present as possible as long as the functions of the othercomponents are not adversely affected. Particularly desirable is a highweight ratio of the phosphate ion to a humectant, so that the bestfeatures of both components are happily combined.

US. Patent No. 3,398,002 to Bondurant et al. discloses a fountainsolution said to be of universal application for planographic printing.The composition of this solution is relatively complex, containing atleast four necessary components (in addition to water) and including,for instance, an alcohol such as ethyl alcohol, propyl alcohol, orisopropyl alcohol, and ethylene glycol monobutyl ether. The lattercomponent in particular is said to undergo a coupling action which isrelied upon to eliminate ink emulsification. Under optimum conditions,the maximum amount of the phosphate ion in the solution of Patent No.3,398, 002 is 10 percent by Weight calculated as the monopotassium,monoammonium, or monosodium phosphate; and the maximum amount ofhumectant is 30 percent by weight.

SUMMARY OF THE INVENTION The aqueous fountain solution of the presentinvention is highly concentrated as to the amount of phosphate ion andhumectant present and, accordingly, has a relatively high weight ratioof phosphate ion to humectant. For example, the present solutionscontain as much as 12 percent by weight of an anhydrous phosphate, suchas monosodium phosphate, and as much as percent by weight of ahumectant.

These relatively concentrated amounts are accomplished, in part, byeliminating from the solution all additives such as alcohols, ethers,etc., which were thought to improve the overall performance of afountain solution. Instead, it has been determined that such additivesactually inhibit the solubility in the aqueous medium of othercomponents and especially those whose presence in maximum amounts havebeen found to be advantageous. The present concentrated fountainsolutions have also been achieved by the use of a buffered phosphatecompound capable of relatively high solubility in the solution to produce a high weight ratio of the phosphate ion to the humectant withoutresulting in a highly acidic pH, even in the concentrated form.

As a result, the present concentrate can be shipped to a point of useand then diluted as needed with water. The amount of the dilutiondepends upon the purpose of use, either as a plate etch or fountainsolution, and on the particular master material and the equipment uponwhich it is run. In any case, the present solution after dilutionperforms well with each type of master and especially with Photo-Directand electrostatic masters which are inherently quite critical in theiroperation, and especially so when running these two types intermixed,and with other types of masters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A concentrated aqueous fountainsolution of the present invention comprises at least 60 percent byweight of a humectant and a suflicient amount of a buifered phosphatecompound to provide a weight ratio of the phosphate ion to the humectantin the range of about 0.085 1 1 to about 0.16021 on the basis ofanhydrous diI-I sodium orthophosphate. The phosphate compound issufliciently buffered to provide a pH for the concentrate in the rangeof about 3.75 to about 4.50 for the stated weight ratios. Theconcentrate may also contain a low molecular Weight aldehyde accordingto US. Patents 2,393,875 and 2,515,- 536.

In view of its hygroscopic character and its aid to viscosity, thehumectant aids in keeping clean the hygrophilic non-image areas of amaster. The humectant may be glycerin, ethylene glycol, or diethyleneglycol. Glycerin is much preferred. Longer runs are possible withglycerin than with the other two, because glycerin increases theviscosity more eifectively. However hygroscopic, the glycerin and wateralone do not provide an acceptable fountain solution. The presence of aphosphate ion is essential.

To place by dissolution sufiicient quantities of the phosphate ion inthe solution concentrate without unduly lowering the acid pH, a bufferedphosphate compound is used. Although the previously mentioned U.S.Patent 3,398,002 teaches that monoammonium phosphate can be used in thatsolution as well as monosodium phosphate, monoammonium phosphate is notuseful in the present fountain solutions. It cannot meet the highersolubility requirements and does not produce the phosphate ion tohurnectant weight ratio desired. Instead, in the present solution,alkali metal phosphate salts, such as sodium and potassium phosphates,that still contain an ionizable hy drogen atom, are used. Althoughdi-substituted phosphoric acid salts, such as disodium acid phosphate,may be used to achieve a phosphate ion to humectant weight ratio inlower portion of the range cited, it is preferred to use themono-substituted salts because of the required pH values. The preferredbuttered phosphate compound is monosodium phosphate which is also knownas diH sodium orthophosphate. The hydrated form of an alkali metal acidphosphate may be used to promote the dissolving action.

The joint presence of the humectant and buffered phosphate compoundtends to encourage the formation of mold. It has been found that themold can be substantially inhibited or entirely eliminated by thepresence of a low molecular weight aldehyde, such as formaldehyde andacetaldehyde. In addition, the aldehyde, especially formaldehyde,materially contributes to the eflicacy of the fountain solution byaiding the cleaning of the hydrophilic, non-image areas of the masterand maintaining them inkrepellent. Further, the aldehyde reduces theratio of fountain solution to ink needed to keep the background clean.If the ratio of fountain solution to ink is high, it tends to cause thecopy paper to curl and the ink to become emulsified. The use of analdehyde guards against these deleterious eifects by reducing the ratioof the fountain solution to ink needed by the master.

With respect to proportions, substantially increased amounts of thehumectant and phosphate ion are jointly possible. The humectant shouldcomprise at least 60 percent by weight of the concentrate and cancomprise as much as 75 percent or higher. Preferably, as much aspossible of the buffered phosphate compound should be dissolved in theconcentrate. Based on solubility limits, the present concentrate candissolve a suflicient amount to provide a phosphate ion to humectantweight ratio in the range of about 0.085 :1 to about 0.160:l on thebasis of anhydrous diH sodium orthophosphate. As indicated, this resultsin a pH range for the concentrate of about 3.75 to about 4.50. Thealdehyde can be present in an amount up to about 3 percent based on a 37wt. percent aqueous solution. More than 3 percent tends to upset thebuttering action of the phosphate.

As an example, a composition of the present concentrate containing thepreferred components may have the following general composition inweight percent:

Percent Glycerin 60 to 75 Monosodium phosphate 8 to 12 Formaldehyde (37%aqueous solution) 0.5 to 2.5 Distilled water Balance Example 1 Aconcentrated fountain solution was prepared having this composition:

Quantities, Percentage kilograms Components 70.00 84. 140 Glycerin,percent. 1.00 1. 202 37% aqueous formaldehyde. 11.50 13. 820 Monosodiumphosphate monohydrate. 17.50 21. 038 Distilled water.

In preparing this concentrate, the monosodium phosphate was first wettedby the formaldehyde to the consistency of a paste. The water was nextadded with stirring to fully dissolve the phosphate. Then the glycerinwas added and the stirring continued until the solution was homogeneous.These quantities produced approximately 25 US. gallons. The specificgravity of this solution was 1.275 at 25/4 centigrade. Its pH was 4.30at 25 centigrade. The concnetrate was packaged for shipment in onegallon plastic bottles made of polyethylene.

Example 2 Another fountain solution concentrate was prepared having thiscomposition:

Component: Percentage Glycerin 65.0 37% aqueous formaldehyde 0.75Monosodium phosphate 8.5 Water Balance The ingredients were mixedtogether with continuous stirring in the manner of the preparation ofthe composition of Example 1. The specific gravity of this concentratewas 1.250 at 25/4 centigrade, and its pH was 4.10 at 25 centigrade.

Example 3 The concentrate of Example 1 was diluted one part of theconcentrate to 7 parts of water and then used as a fountain solution ina duplicator having separate ink and water systems. An electrostaticmaster was used which normally produced about 500 copies before thebackground of the master degraded to ink receptiveness. With the presentfountain solution, diluted as indicated, the same electrostatic masterproduced over 5000 copies. It was also noted that an increased number ofelectrostatic masters could be run on a duplicator having a blanketcleaner, before a sufiicient amount of sludge was deposited on the wickin the blanket cleaner to require cleaning of the wick.

Example 4 In a duplicator having an integrated ink and water system, theconcentrate of Example 1 was diluted one part of the concentrate to 3parts of water, and then used as a fountain solution for a succession ofelectrostatic masters. It was found that more masters could be run thanusual before clean-up of the inking system was required.

Example 5 The present concentrate diluted as in Example 3 was used as afountain solution for a Photo-Direct master on a duplicator havingseparate systems. This master ran easily and was compatible with alldirect image masters and electrostatic masters.

Example 6 masters without losing its ability to keep clean the back-'ground or hydrophilic areas of the masters. In particular, the presentconcentrate provides increased operating latitude; interchangeabilityand operating compatibility among conventional, electrostatic,Photo-Direct, and direct image masters; and especially much longer runswhen used with electrostatic masters.

The present fountain solution concentrate has an im proved desensitizingeffect which requires less moisture to produce quality copies. Becausethere is less solution used, the possibility of contamination is reducedsince less moisture is carried back into the ink system. The presentconcentrate also makes longer runs possible through its special chemicalproperties that provide the best combination of action for keepingnon-image areas of the masters clean with a minimum of moisturepentration of the surface of the master. Ink and water balance are easyto maintain, and emulsification of the ink is also reduced. In order toachieve the appreciably increased amounts of the phosphate ion andhumectant in the concentrate, the present solutions eliminate otherpreviously used compoents like alcohol and ethers which delimit thesolubility of the phosphate and the humectant.

Although the foregoing describes several embodiments of the presentinvention, it is understood that the invention may be practiced in stillother forms within the scope of the following claims.

What is claimed is:

1. A solution concentrate of increased operating latitude adapted uponvarying degrees of dilution for use with a plurality of different typesof planographic masters, said concentrate consisting essentially of anaqueous solution of about percent to about percent by weight of ahumectant selected from the group consisting of glycerin, ethyleneglycol, and diethylene glycol, and a sufiicient amount of a buffered,ionizable, hydrogen-containing, alkali metal phosphate to provide aweight ratio of the phosphate ion to said humectant in the range ofabout 0.085 :1 to about 0.16021, said phosphate being sufiicient- 1ybuttered to provide a pH for said concentrate in the range of about 3.75to about 4.50 for the stated weight ratios.

2. The solution concentrate of claim 1 wherein said buffered alkalimetal phosphate is a diH sodium orthophosphate.

3. A solution concentrate of increased operating latitude adapted uponvarying degrees of dilution for use with a plurality of different typesof planographic masters, said concentrate consisting essentially inweight percent of:

Percent Glycerin 60 to 75 diH sodium orthophosphate 1 8 to12Formaldehyde (37% aqueous solution) 0.5 to 2.5 Water Balance Based onanhydrous orthophosphate.

4. A solution which is to be diluted with water for use as a plate etchand in the fountain of a planographic printing press, consistingessentially of:

60-75 wt. percent of a humectant selected from the group consisting ofglycerin, ethylene glycol and diethylene glycol,

O-3 Wt. percent (calculated on the basis of a 37 wt. percent aqueoussolution) of an aldehyde selected from the group consisting ofacetaldehyde and formaldehyde, and

as the sole source of phosphate ion, from 8-12 wt. percent (calculatedon an anhydrous basis) of a buffer selected from the group consisting ofmono and diH, sodium and potassium orthophosphates, and their hydrates.

References Cited UNITED STATES PATENTS LORENZO B. HAYES, PrimaryExaminer U.S. Cl. X.R. l0145 1

